Before the image grid can correctly pull your images from your listings you have to make sure of two things:
Ensure Terms Have Content
Your chosen taxonomy (listing region, listing category, etc) has to have at least 1 listing. If your chosen taxonomy does not have a listing associated with it, the image grid will not show it on the front page.
Ensure Listings Have Attached Images
At least 1 of those listings has to have an image “attached” to it. This means that either the featured image or a gallery image must be directly uploaded from the listing submission page itself. This can be done from the back-end or the front-end.